Light source automatically fitting to object
This solution is different to what you asked, but I think it gets the intended result.

The sun light itself will impact 'every' object without needing to be attached to every object. The sun has constant direction parallel rays regardless of where it is placed, unlike the other light sources that are relative to their position.  So for example, in the following three images, the sun is above, moved just right and then moved far below and yet they produce the same constant result for the object. For every other object I add in the scene, the same sun light properties will be applied.  

Adding a light per object is most likely an overkill.

Above:



To the right:



Well below: